Heat Test Yr 9

Question 1

Convection

Answer 1

-main method of thermal energy transfer in fluids
-in fluids, particles are free to move, and energy is transferred as they move

Question 2

Convection cycle

Answer 2

-cold air near the radiator warms up and expands

-air is less dense > moves upwards

-energy is transferred between the rising warm air + the cold air surrounding it

-cooler air contracts and becomes more dense > it sinks downwards

-colder air moves towards the radiator

Question 3

Leslie cube experiment

Answer 3

1. Place Leslie cube on heat-proof mat.
2. Fill cube with boiling water and replace lid.
3. Use infra-red detector on one side; wait for reading to settle and record it.
4. Repeat for each side, keeping detector at same distance.

Question 4

Leslie cube results

Answer 4

Matt black: 89.9°C
Shiny black: 87°C
Matt white: 82.3°C
Shiny silver: 28.6°C

Question 5

Why do darker surfaces absorb more heat?

Answer 5

-they absorb a wider range of wavelengths of light
-and converts them into heat

Question 6

Why do shiny surfaces reflect heat?

Answer 6

-they have a high albedo
-meaning the reflect a lot of heat

Question 7

Which surface is the best emitter of heat?

Answer 7

-reflective surfaces

Question 8

Radiation

Answer 8

-method of transferring energy as a wave

Question 9

What things emit infra-red radiation?

Answer 9

-all hot (or warm) things emit infra-red radiation
-hotter things emit more

Question 10

An object hotter than its surroundings will emit more radiation (each second), than it absorbs, in order to cool down. True or False?

Answer 10

True

Question 11

When the rate of emission is the same as the rate of absorption…

Answer 11

…the temperature of the
object does not change. This state is called thermal equilibrium.

Question 12

Evaporation

Answer 12

-when a liquid changes to a gas
>e.g. wet clothes on a washing line in fine weather will gradually dry off

Question 13

When does evaporation take place?

Answer 13

-from the surface of the liquid at all temperatures

Question 14

What factors affect the rate of evaporation?

Answer 14

-increasing surface area of the liquid
-creating more movement of air across liquids surface

Question 15

Why do we feel cold when we get out of the pool?

Answer 15

-evaporating liquid requires energy
>this energy is taken from the skin and the skin feels cold

Question 16

Specific heat capacity

Answer 16

-the energy required to raise the temperature of 1 kg by 1°C

Question 17

What materials usually tend to have low heat capacities?

Answer 17

-metals

Question 18

Specific heat capacity equation

Answer 18

c = ΔE/mΔθ (change in energy over mass times change in temperature)

Question 19

SHC: ΔΕ=…

Answer 19

…mcΔΘ

Question 20

*shc Heat Energy (J) =

Answer 20

mass (kg) x SHC x temp. change (°C)

Question 21

When the temperature of a system is increased by supplying energy to it, the increase in temperature depends on:

Answer 21

-mass of substance
-material of substance
-energy put into the system

Question 22

Specific heat capacity of water

Answer 22

4200J/kg

Question 23

Why is it helpful that we are mostly made out of water?

Answer 23

-body temperature doesn’t increase too much during exercise and doesn’t cool too quickly when its cold

Question 24

What are things with high specific heat capacities used for?

Answer 24

-house central heating systems
e.g. hot water flows through radiators, but if it had low shc it would cool down before it got to radiators

Question 25

What are things with low specific heat capacities used for?

Answer 25

-kitchen appliances > they can cool down and warm up quickly, very efficient for cooking

Question 26

Specific latent heat

Answer 26

-the energy required to change the state of 1 kg of a substance

Question 27

Specific latent heat of fusion

Answer 27

-energy required to change of 1kg of a solid into liquid (at same temp.)

Question 28

Specific latent heat of vaporisation

Answer 28

-energy required to change 1kg of a liquid into gas (at same temp.)

Question 29

Specific latent heat equation

Answer 29

L= E/M (energy over mass)

Question 30

SLH: ΔΕ =...

Answer 30

...mL (mass x latent heat)

Question 31

# Heater, joulemeter, heatproof mat Latent heat of vaporisation experiment

Answer 31

1. Place beaker of water on a balance (heatproof mat). 2. Bring water to boiling point using heater; joulemeter will reset to zero at boiling point. 3. Heater is then allowed to boil water for 5 minutes. 4. Record measurements: >Joulemeter reading: 60kJ >Mass at start: 968g >Mass after 5 min: 944g

Question 32

Specific heat capacity copper experiment

Answer 32

1. Record mass of copper block (kg). 2. Place heater in larger hole of the block. 3. Connect ammeter, power pack, and heater in series. 4. Connect voltmeter across power pack: _____________________(V)__________________ I I I I __________________ 12V __________________ I I I __________________(A)____________________ I 5. Insert thermometer in other hole. 6. Switch power pack to 12V and turn on. 7. Record ammeter (3.7A) and voltmeter readings (12V) - constant throughout. 8. Start stopwatch and measure temperature every minute. 9. Log results in table. 10. Calculate work done: Work (J) = Amps x Volts x Time (s).

Question 33

Solid -> Gas

Answer 33

-sublimination

Question 34

# heater Specific latent heat experiment (ICE THING)

Answer 34

_ * ENERGY METREPOWER SUPPLY \ I / \ / \ ICE / \ / I I I I I I I I I I I I I I I _____________________________I 1. Record mass of empty beaker 2. Switch on heater. 3. Collect water in beaker. 4. Record energy using power pack. 5. Weigh beaker to find mass of water.

Question 35

Why does evaporation take place from the skin, making the rest of the object colder?

Answer 35

-there are attractive forces between molecules and only the fastest molecules have enough energy to break away from others >so when they escape, they lower the average speed/energy in kinetic store >the lower average speed/energy in kinetic store, the lower the temp. of the object